Recent epidemiologic studies indicate that chronic exposure to inhalation anesthetic gases may have a deleterious effect on the health of personnel employed in the operating room. A comprehensive study of exposed personnel in the hospital operating room of this country was recently conducted by the American Society of Anesthesiologists for the National Institute for Occupational Health and reported in 1974. This major study confirmed the findings of previous small-scale studies, all of which indicated an increase in the rate of spontaneous abortion and birth defects in exposed operating room personnel. There was also a significant increase in the incidence of liver disease and unexpected disclosure of a higher rate of congenital anomalies in unexposed wives of practicing anesthesiologists. The belated suspicion that a large segment of the dental profession might be similarly effected was given support when a small pilot study of dentistry disclosed similar serious health hazards. The purpose of the present investigation is to study in detail the health histories of dentists, their wives, and auxiliary personnel numbering nearly 100,000 individuals. A unique opportunity in this effort will be the study of a large occupational group exposed to a single agent, nitrous oxide, versus the anesthetic gas mixtures. A two-phase questionnaire survey has been designed to first identify those dentists who use and those who do not use inhalation anesthetics. The investigation will then concentrate on the health hazards of the users, ther wives and exposed employees. In turn, this group will be compared to a control group of non-inhalation anesthetic users. A carefully designed written questionnaire, fashioned after that used in the original ASA-NIOSH survey of hospital operating room personnel, will be employed. The questionnaire will be followed by written and telephone communications, ensuring a high response rate and adding validity to the overall health findings.